Method and apparatus for processing chopped fibers from continuous tows

ABSTRACT

An apparatus for processing chopped fibers from essentially continuous tows, each consisting of individual strands, comprises selectively feeding at least two tows to a venturi pump and associated cutter mechanism where the tows are cut or chopped into relatively short lengths to form chopped fibers. The apparatus includes sensors for monitoring the movement of each of the tows to the pump and cutter mechanism, and a controller which adjusts the feed rate of the tows and the rate of operation of the cutter mechanism in the event movement of one of the tows varies from a predetermined feed rate.

FIELD OF THE INVENTION

This invention relates to an apparatus for processing chopped fibers,and, more particularly, to a method and apparatus for chopping orcutting one or more essentially continuous tows, each consisting ofindividual strands, into relatively short fibers of predetermined lengthwhich are dispensed at an accurately controlled feed rate onto or into asubstrate such as the nonwoven pad of a hygienic article.

BACKGROUND OF THE INVENTION

Hygienic articles such as disposable diapers, sanitary napkins,incontinence pads and sick bed sheets must have a high absorptioncapacity to effectively retain eliminated body fluids for acceptableperiods of time. Early hygienic articles of this type employed cellulosewadding, fluff cellulose or absorbent cotton as absorbent materials. Theproblem with these materials is that their moisture-retaining capacityis relatively small compared to their volume. In order to improve themoisture-retaining capacity of hygienic articles made from thesematerials, the volume of such absorbent materials in the hygienicarticle must be increased. This produces a bulky product which isunacceptable in many hygienic articles, particularly sanitary napkins.

In an effort to reduce the volume and size of hygienic articles, andincrease their absorbent capacity, fluid absorbent substrates have beendeveloped in which highly absorbent materials are combined within thefiber structure of cellulose fluff, wood pulp, textile fibers or othernonwoven fibrous materials. Many substantially water-insoluble absorbentpolymers having a high capacity for absorbing water and body fluids havebeen developed in recent years for enhancing the moisture-absorbentcapability of hygienic articles. These polymers are partially or whollysynthetic and are commercially available in fine grain, particulate formor in continuous tows consisting of a number of individual strands. See,for example, U.S. Pat. Nos. 3,997,484; 3,661,815; 4,117,222; and,3,936,441.

A number of systems have been developed for incorporating amoisture-absorbent material in the nonwoven layer or pad of a hygienicarticle, such as a disposable diaper, as discussed in U.S. Pat. Nos.4,927,346 and 5,017,324 owned by the assignee of this invention. In theparticular system disclosed in U.S. Pat. Nos. 4,927,346 and 5,017,324,highly moisture-absorbent material in fine grain particulate form isincorporated within the nonwoven pad of a hygienic article within aforming chamber. A perforated conveyor is movable between the inlet andoutlet of the forming chamber above a duct which is connected to asource of vacuum. Nonwoven fibers formed of cellulose fluff, wood pulpor other nonwoven materials are introduced into the forming chamberthrough a conduit and drawn onto the perforated conveyor by operation ofthe vacuum source. As the nonwoven material is drawn atop the conveyor,one or more spray guns located within the forming chamber intermix thehighly moisture-absorbent material with a portion of the fibrous,nonwoven material to form a nonwoven pad having moisture-absorbentmaterial interspersed throughout a predetermined portion of itsthickness while leaving other portions of the pad substantially free ofhighly moisture-absorbent material. In the formation of a disposablediaper, for example, the nonwoven pad containing the moisture-absorbentmaterial is subsequently attached to a thin layer of polyethylene whichforms the backing sheet of the finished article.

Currently available hygienic articles, such as disposable diapers, aremanufactured with systems of the type described above using highlymoisture-absorbent material in fine grain, particulate form. Despiteefforts to locate the highly moisture-absorbent particulate material atselected areas within the thickness of a nonwoven pad of such articles,there have nevertheless been problems attributable to the form of themoisture-absorbent material. It has been found that the particles ofhighly moisture-absorbent material tend to sift through the nonwovenfibers of the nonwoven pad and can be lost through the perforatedconveyor within the forming chamber. Particulate, moisture-absorbentmaterial is difficult to contain, even with a filtering systemassociated with the forming chamber, and environmental contamination canresult. Sifting or migration of particulate moisture-absorbent materialthrough the nonwoven fibers is also a problem within the finishedhygienic article. It is not uncommon for the moisture-absorbentparticles to sift through the nonwoven layer and concentrate at thepolyethylene backing sheet of a disposable diaper, for example,producing an undesirable rough, granular feel to the diaper.

Another problem with the use of highly moisture-absorbent material ingranular or particulate form within hygienic articles is the speed atwhich it absorbs urine or other body fluids. While capable of absorbingmoisture many times its weight, particles of highly moisture-absorbentmaterial have a relatively small surface area and body fluids must comeinto contact with such particles in order to be absorbed. Even if arelatively large quantity of particulate moisture-absorbent material isprovided within a hygienic article, there are nevertheless spaces orareas within the nonwoven pad with lesser concentrations of particlesand therefore a longer time period is required before such moisture orbodily fluids can be absorbed.

SUMMARY OF THE INVENTION

It is therefore among the objectives of this invention to provide amethod and apparatus for depositing highly moisture-absorbent materialinto the nonwoven layer or pad of hygienic articles such as disposablediapers which substantially reduces loss of moisture-absorbent material,which eliminates unwanted migration of moisture-absorbent materialwithin the finished article, which provides for rapid absorbency ofbodily fluids or other moisture and which provides an accurately meteredvolume of moisture-absorbent material.

These objectives are accomplished in a method and apparatus for formingchopped fibers of highly moisture-absorbent material from essentiallycontinuous tows each consisting of individual strands ofmoisture-absorbent material. At least two tows are independently fed toa venturi pump and associated cutter mechanism where the tows are cut orchopped into relatively short lengths to form chopped fibers, and arethen discharged to a forming chamber, for example, of the type disclosedin U.S. Pat. Nos. 4,927,346 and 5,017,324. The apparatus includessensors for monitoring the movement of each of the tows to the pump andcutter mechanism, and a controller which adjusts the feed rate of thetows and the rate of operation of the cutter mechanism in the eventmovement of one of the tows is interrupted or discontinued.

In the presently preferred embodiment of this invention, a total ofthree tows are supplied from separate containers or hoppers to a primaryfeed roller rotated by a variable speed motor. Each of the tows isforced against the feed roller by a separate pressure roller which ismovable between an extended position in which it engages the feed rollerand a retracted, disengaged position. Each tow is individually advancedfrom the primary feed roller to a secondary feed roller, driven by avariable speed motor, at which a second set of pressure rollers, one foreach tow, is provided. The tows are advanced from the secondary feedroller into separate guide tubes of a cutter mechanism located at theinlet of the venturi pump, which applies a continuous negative pressureto the tows. As described below, each tow is cut into chopped fibers ofuniform length by the cutter mechanism and then discharged from the pumpinto, for example, the forming chamber for the nonwoven pad of ahygienic article.

The primary and secondary feed rollers are rotated by their respectivevariable speed motors at a predetermined rate, corresponding to the linespeed of the hygienic article line, for example, to ensure that anaccurately metered quantity of chopped fibers of highlymoisture-absorbent material is provided. The cutter mechanism has acutter blade mounted to the drive shaft of a third variable speed motorwhich is operative to control the speed of rotation of the cutter bladein timed relation to the feed rate of the tows from the secondary feedroller. The feed rate of the tows into the cutter mechanism, and thespeed of rotation of the cutter blade, determine the length of the fibertows discharged from the pump.

One important aspect of this invention is the provision of sensingdevices and control means to ensure that a substantially constant feedrate or volume of chopped fibers of uniform length is maintained, evenif the supply of one or more of the tows is slowed, interrupted,discontinued or otherwise varied for any reason. This is particularlydesirable in the application of introducing highly moisture-absorbentmaterial into the nonwoven pad of hygienic articles where the quantityof moisture-absorbent material must be closely controlled and highproduction speeds require minimal interruption in the supply ofmoisture-absorbent material.

In the presently preferred embodiment, sensors are provided upstreamfrom the primary feed roller to detect the movement of each of the towsthereto. Another set of sensors is provided between the primary andsecondary feed rollers to sense the presence and movement of the towstherebetween, and additional sensors are placed at the inlet to thecutter mechanism. In the event any one of these sensors detects anabsence of movement, movement of one or more of the tows below apredetermined rate or any other variation in feed rate, an operationalsequence is initiated to ensure that the quantity of the fibersdischarged from the venturi pump remains substantially unchanged.

For example, assuming the movement of one of the three tows isinterrupted or stopped for some reason, a controller operates to moveeach of the two pressure rollers associated with that tow, i.e., one ateach of the primary and secondary feed rollers, to a retracted positionaway from such feed rollers. A clamping mechanism associated with suchtow, located between the secondary feed roller and the venturi pump, isthen activated to clamp such tow in a fixed position. In order to makeup for the reduced volume of material entering the cutter mechanism andventuri pump due to the absence of one tow, the controller operates thevariable speed motors to increase the speed of rotation of both theprimary and secondary feed rollers so that the remaining two tows areadvanced to the cutter mechanism and venturi pump at a higher rate ofspeed. At the same time, the controller operates the third variablespeed motor to increase the speed of rotation of the cutter blade at arate corresponding to the faster pace at which the two tows are beingdelivered to the cutter mechanism. As a result, the cutter mechanismcuts each of the remaining two tows to form chopped fibers havingsubstantially the same length as those previously formed with the threetow supply, and the overall volume or quantity of chopped fibersdischarged from the venturi pump is maintained substantially constantbecause of the increased feed rate of the remaining two tows.

In the particular application of forming the nonwoven pad of adisposable diaper, it is advantageous to deposit the highlymoisture-absorbent material at longitudinally spaced locations along thenonwoven pad. This is accomplished in the system of this invention bythe operation of the primary and secondary feed rollers herein.Preferably, a loop or excess length of each tow is allowed to formbetween the primary feed roller and a secondary feed roller so that thetension of the tows into the secondary feed roller can be controlled. Inorder to obtain an intermittent supply of chopped fibers into theforming chamber for the nonwoven pad of the hygienic article, thesecondary feed roller is preferably rotated intermittently, i.e., itsrotation is quickly started and stopped by the associated variable speedmotor, so that the supply of the tows to the cutter mechanism andventuri pump is discontinuous. The venturi pump is continually operated,or, alternatively, can be started and stopped with the secondary feedrollers, so that a vacuum is applied to the tows fed thereto. As aresult, the chopped fibers are discharged from the outlet of the venturipump in accordance with the rate at which the tows are advanced from thesecondary feed roller.

In another aspect of this invention, the venturi pump and associatedcutter mechanism are constructed to chop or cut the individual strandsof each tow to form chopped fibers of substantially uniform length, andto smoothly transmit these chopped fibers without bunching up throughthe venturi pump. In the presently preferred embodiment, the venturipump comprises a pump body formed with an inlet passageway and anintersecting throughbore having opposed ends. A nozzle is mounted at oneof the ends of the throughbore having an inlet adapted to connect to asource of pressurized air, and an outlet which discharges thepressurized air generally perpendicularly to the inlet passageway of thepump body and into a venturi passageway which forms the outlet of theventuri pump. A number of nozzle constructions are disclosed in thefollowing detailed description, each of which creates a vacuum ornegative pressure within the inlet passageway of the pump body to drawthe tows from the secondary feed roller into the cutter mechanism and tosmoothly convey the chopped fibers formed by the cutting mechanismthrough the venturi passageway and out of the pump body.

The cutting mechanism of this invention is mounted to the pump body ofthe venturi pump in communication with its inlet passageway. In thepresently preferred embodiment, the cutting mechanism includes atapered, tow guide tube for each of the tows which communicate withseparate tow slots formed in a cutter plate. The tow guide tubes taperinwardly from a larger diameter inlet end to a substantiallyrectangular-shaped outlet end having the same cross section as the towslots in the cutter plate. In the course of movement through the towguide tubes into the tow slots, each tow is "opened" or spread from agenerally circular cross section to a rectangular cross section in whichthe individual strands of each tow are located substantiallyside-by-side with at least some spacing therebetween. This opening orspreading of the tow is attributable not only to the shape of the towguide tubes, but also to a pressure differential created between the towguide tubes and the area within the cutting mechanism at which the towsare cut.

Preferably, three extensions or ribs are formed at the base of thecutter plate and a tow slot is formed in the cutter plate at each rib. Adouble-edged cutter blade is mounted at the end of the shaft of thethird variable speed motor in position where its two cutting edges arerotated immediately adjacent the tow slots in the ribs of the cutterplate. Each fiber tow is directed through the guide tubes and tow slotsin the cutter plate such that a portion of the tows extend below theribs of the cutter plate where they are sheared by the cutting edges ofthe cutter blade. Because the tows are flattened or opened by the towguide tubes, most of the individual strands in each tow are directlycontacted and cut by the cutter blade, instead of being hidden behindone other, which results in a clean, accurate separation of the strandsfrom the remainder of the tow. This aids in producing chopped fibershaving substantially uniform length.

In the particular application of forming chopped fibers from tows ofhighly moisture-absorbent material, the individual strands forming eachtow are relatively lightweight and difficult to smoothly transferwithout bunching up from the area at which they are cut to the outlet ofthe pump. In order to obtain a smooth transfer of the tows and choppedfibers through the pump, the cutter plate and cutter blade of thecutting mechanism herein are designed to control the vacuum applied tothe tows during the cutting operation and provide a flow path away fromthe area of the cutter blade toward the pump outlet. As mentioned above,the bottom of the cutter plate is formed with three outwardly extendingribs each formed with a rectangular-shaped tow slot which defineopposed, elongated shear edges. The individual strands of each tow aresimultaneously cut at these shear edges in the ribs as a cutting edge ofthe cutter blade moves therepast. Unlike the cutting action of a pair ofscissors, for example, the cutter blade of this invention is movablewith respect to the tow slots of each rib such that each cutting edge ofthe cutter blade is substantially parallel to one of the opposed shearedges of the tow slot at the time such cutting edge contacts the strandsof a tow. As this cutting operation occurs, the remainder of the towslot in the rib is covered by the cutting blade. This momentarilyinterrupts the application of vacuum upstream from the cutter plate,i.e., within the tapered guide tubes of the cutting mechanism, whichensures that the newly formed chopped fibers are cleanly separated fromthe remainder of the tow and immediately directed away from the cutterplate and cutter blade along a flow path leading into the venturi outletof the pump. This feature of the present invention provides for smoothhandling of the chopped fibers, and substantially prevents theirbunching up within the tow slots in the cutter plate at the time ofseparation from the remainder of the tow, or in the course of passagefrom the area of the cutter plate to the outlet of the pump.

DESCRIPTION OF THE DRAWINGS

The structure, operation and advantages of the presently preferredembodiment of this invention will become further apparent uponconsideration of the following description taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a schematic view of the overall apparatus of this invention;

FIG. 1A is a schematic view of an alternative embodiment of theapparatus shown in FIG. 1;

FIG. 2 is a disassembled perspective view of the cutter mechanism hereinmounted to the venturi pump;

FIG. 3 is a cross sectional view of a portion of the cutter mechanismillustrating the passage of one tow therethrough;

FIG. 4 is a cross sectional view of one tow taken generally along line4--4 of FIG. 3;

FIG. 5 is a cross sectional view of the tow of FIG. 4 taken generallyalong line 5--5 of FIG. 3;

FIG. 6 is a cross sectional view of the tow of FIGS. 4 and 5 takengenerally along line 6--6 of FIG. 3;

FIG. 7 is a cross sectional view taken generally along line 7--7 of FIG.3 showing a tow cutting operation;

FIG. 8 is a bottom view of the cutter plate and cutter blade takengenerally along line 8--8 of FIG. 3;

FIG. 9 is a cross sectional view taken generally along line 9--9 of FIG.2 showing a portion of the venturi pump herein;

FIG. 9A is a view similar to FIG. 9 with the addition of a flow sensorto sense the movement of fibers therethrough;

FIG. 10 is a cross sectional view of an alternative embodiment of anozzle for use with the venturi pump shown in FIG. 9;

FIG. 11 is an alternative embodiment of the nozzle shown in FIGS. 9 and10;

FIG. 11A is a cross sectional view taken along lines 11A--11A of FIG.11;

FIG. 12 is a still further embodiment of a nozzle adapted for use withthe venturi pump of FIG. 9;

FIG. 13 is a view of an outlet tube, in partial cross section,insertable within the outlet in the pump body of FIG. 9;

FIG. 14 is a schematic, elevational view of a portion of the apparatusof FIG. 1, adapted for use with a forming chamber employed to make thenonwoven pad of the hygienic article;

FIG. 15 is an enlarged, partial view of the nonwoven pad being formedwithin the forming chamber illustrated in FIG. 14; and

FIG. 16 is a plan view of a nonwoven pad made in the forming chamber ofFIG. 14 wherein chopped fibers of moisture-absorbent material aredisposed at selected areas along the length thereof.

DETAILED DESCRIPTION OF THE INVENTION

One presently preferred embodiment of the chopped fiber processingapparatus 10 of this invention is schematically illustrated in FIG. 1.As discussed in more detail below in connection with a description ofFIGS. 14-16, the apparatus 10 herein can be particularly adapted tointermix chopped fibers 12 of a highly moisture-absorbent materialwithin a predetermined portion of the thickness of a nonwoven layer orpad 14 of a hygienic article such as a disposable diaper. For purposesof the present discussion, the structure and method of operation ofapparatus 10 is described in conjunction with the formation of choppedfibers 12 from tows 18a, b and c each formed of essentially continuous,individual strands 20 (see FIGS. 6 and 7) of highly moisture-absorbentmaterial of the type disclosed, for example, in U.S. Pat. Nos.3,997,484; 3,661,815; 4,117,222; and, 3,936,441. It should beunderstood, however, that the apparatus 10 of this invention could beemployed with a variety of materials and is capable of producing choppedor cut sections or fibers of relatively short length from an essentiallycontinuous supply of material such as graphite, aramid, fiberglass andthe like in the form of a tow, roving, strand or the like. The followingdiscussion of the operation of the apparatus 10 is therefore not limitedto the formation of chopped fibers of highly moisture-absorbent materialfor use in manufacturing disposable diapers, but is useful in a varietyof other, non-hygienic article applications.

The overall construction of apparatus 10 is initially described,followed by a discussion of the venturi pump 22 and cutter mechanism 24of the apparatus 10.

Overall Construction of Embodiment of FIG. 1

Referring to FIG. 1, the apparatus 10 comprises an operator control 26,a combined pneumatic, electrical and flow controller 28 connected byline 29 to operator control 26, a motor control 30 connected by line 31to operator control 26 and various tow handling and sensing devicesdescribed individually below. The operator control 26 comprisesessentially an interface between the controller 28, motor control 30 andthe manufacturing line to which the chopped fibers 12 are directed fromthe venturi pump 22. In the particular example of the formation ofdisposable diapers, for example, the operator control 26 provides aninterface between the controller 28, motor control 30 and a conveyor 32upon which the nonwoven layer or pad 14 of the disposable diaper isformed as described below. See FIG. 14. This interface is necessary inorder to ensure that the feed rate or volume of chopped fibers 12, andthe length of such fibers 12, is maintained substantially constantregardless of the speed of operation of the conveyor 32.

In the presently preferred embodiment, the three tows 18a, b, c aresupplied from separate tow hoppers 34a, b, c through individual feedchannels 36a, b, c to a primary feed roller 38. The primary feed roller38 is connected to the drive shaft 40 of a variable speed, primary motor42 which is connected by control line 41 to the motor control 30. Eachof the tows 18a, b, c is fed between the primary feed roller 38 andpressure rollers 44a, b, c, respectively. These pressure rollers 44a, b,c are each carried by a separate bracket 46 and are connected to thecylinder rod 47 of pneumatic cylinders 48a, b, c, respectively. Thepneumatic cylinders 48a, b, c are each connected by a separate air line50a, b, c, respectively, to controller 28, and their cylinder rods 47are movable between an extended position in which the pressure rollers44a, b, c force the tows 18a, b, c against the primary feed roller 38,and a retracted position in which the pressure rollers 44a, b, c areeach spaced from the primary feed roller 38.

The tows 18a, b, c are transmitted from the primary feed roller 38 to asecondary feed roller 52. Preferably, an excess length or loop 54 ofeach of the tows 18a, b, c is permitted to form between the primary andsecondary feed rollers 38, 52 to control the tension of the tows 18a, b,c as they enter the secondary feed roller 52 for purposes describedbelow. The secondary feed roller 52 is connected to the drive shaft 56of a variable speed, secondary motor 58 whose operation is controlledvia line 59 by motor control 30. Each of the tows 18a, b, c areselectively driven at the secondary feed roller 52 in the same manner asdescribed above in connection with the primary feed roller 38. Threepressure rollers 60a, b, c are mounted on separate brackets 62 beneaththe secondary feed roller 52 in a position to engage the tows 18a, b, c,respectively. The pressure rollers 60a, b, c are moved between anextended position in which they force tows 18a, b, c against thesecondary feed roller 52, and a retracted position spaced from secondaryfeed roller 52, by operation of pneumatic cylinders 64a, b, c,respectively, each having a cylinder rod 65 connected to a pressureroller 60a, b, c. The pneumatic cylinders 64 are operatively connectedby pneumatic lines 66a, b, c to the controller 28.

With the pressure rollers 60a, b, c in an extended position, the tows18a, b, c are advanced from the secondary feed roller 52 and positivelydrawn into the cutter mechanism 24 by a vacuum or negative pressuredeveloped within the venturi pump 22. In the presently preferredembodiment, pneumatic clamps 68a, b, c, illustrated schematically inFIG. 1, are interposed between the secondary feed roller 52 and cuttermechanism 24. These pneumatic clamps 68a, b, c are connected by separatepneumatic lines 70a, b, c to the controller 28 and are selectivelyoperative to clamp tows 18a, b, c, respectively, in a fixed position forpurposes to become apparent below. The tows 18a, b, c pass throughclamps 68a, b, c and enter individual tow inlet tubes 72a, b, c,respectively, which are connected to an inlet cone 74 housing the cuttermechanism 24 described below. This inlet cone 74 is mounted to the pumpbody 76 of the venturi pump 22, which also includes an air inlet 78connected by an air line 80 to the controller 28 and a chopped fiberoutlet 82.

As described below in connection with a discussion of the operation ofapparatus 10, an important aspect of this invention is the provision ofstructure for sensing the movement of each of the tows 18a, b, c throughthe apparatus 10 from the tow hoppers 34a, b, c to the venturi pump 22.A number of sensor devices are provided for this purpose which arelocated at various positions along the run of the tows 18a, b, c throughapparatus 10. Beginning at the lefthand side of FIG. 1, each of the towhoppers 34a, b, c is provided with a level sensor 84, one of which isschematically depicted. Each level sensor 84 is operative to sense thelevel of the tows 18a, b, c within the respective hoppers 34a, b, c, andsend a corresponding signal through separate lines 86a, b, c to thecontroller 28. One presently preferred level sensor 84 is commerciallyavailable from Nordson Corporation of Amherst, Ohio, the assignee ofthis invention, under Model No. 601371.

Immediately upstream from the primary feed roller 38 are movementsensors 88a, b, c, preferably mounted to the feed channels 36a, b, c,respectively, associated with the tows 18a, b, c. Each of these movementsensors 88a, b, c is connected by a separate line 90a, b, c,respectively, to the controller 28 and is operative to provide a signalto the controller 28 in the event the speed of a tow 18a, b, c movingtherepast falls below a predetermined feed rate. One type of movementsensor which is suitable for use herein is depicted in FIG. 9A, and isdescribed below in connection with a discussion of the structure andoperation of venturi pump 22.

The individual strands 20 forming the tows 18a, b, c (see FIGS. 4-6) arelightweight and relatively "fluffy" in their commercially availableform. Preferably, the primary and secondary feed rollers 38, 52, as wellas the pressure rollers 44a, b, c and 60a, b, c, are coated with anon-stick surface to discourage adherence of any of the tow strands 20thereto. Nevertheless, it is contemplated that at least some of thestrands 20 may adhere either to the feed rollers 38, 52 or pressurerollers 44, 60 at some point during the operation of apparatus 10.Material build-up sensors 92 are therefore provided at both the primaryfeed roller 38 and secondary feed roller 52, and additional materialbuild-up sensors 94a, b, c are provided at each of the pressure rollers44a, b, c and pressure rollers 60a, b, c. Suitable material build-upsensors 92 for the feed rollers 38 and 52 are commercially availablefrom Banner Engine of Minneapolis, Minn. under Part No. SE61RNC andSE61E, and suitable material build-up sensors 94a, b, c for the pressurerollers 44a, b, c and 60a, b, c are commercially available from Turck,Inc. of Minneapolis, Minn. under Part No. BIM-IKT-AN6X/KLI-1. Thefunction of the sensors 92, 94 is to detect the presence of aninordinate build up of tow strands 20 on the feed rollers 38, 52, orpressure rollers 44, 60, and send signals to the controller 28 throughlines 96 connected to each sensor 92 and lines 98a, b, c connected toeach set of sensors 94a, b, c.

As mentioned above, a loop 54 is preferably maintained in each of thetows 18a, b, c between the primary and secondary feed rollers 38, 52. Inthe presently preferred embodiment, three loop sensors 100 (only one ofwhich is shown) connected by lines 102a, b, c to controller 28, islocated between the feed rollers 38 and 52 to detect the presence of aloop 54 for each tow 18a, b, c. It is contemplated that these loopsensors 100 may be standard optical sensors, for example, or any othertype of position sensor. One type of sensor which is suitable for thispurpose is a measuring light curtain system available under the tradename "Beam-A-Ray" from Banner Engine of Minneapolis, Minn., Part No.BME/BMR.

With reference to the righthand portion of FIG. 1, two sets of sensorsare associated with the venturi pump 22 and cutter mechanism 24 of thisinvention. In the presently preferred embodiment, a flow sensor 104a, b,c is mounted to the tow inlet tubes 72a, b, c, respectively, to detectmotion of the tows 18a, b, c, therethrough. These sensors 104a, b, c areconnected to controller 28 by separate lines 106a, b, c. Suitablesensors for this purpose are described below in connection with adiscussion of venturi pump 22 and FIGS. 9 and 9A. Additionally, theoutlet 82 of venturi pump 22 is equipped with a discharge flow sensor108, connected by a line 109 to controller 28, for detecting the volumeof chopped fibers 12 emitted from venturi pump 22. A sensor suitable forthis purpose is shown in FIG. 9A and described below.

Alternative Embodiment of FIG. 1A

With reference to FIG. 1A, an apparatus 300 is illustrated which isidentical to apparatus 10 of FIG. 1 except the feed channels 36a, b, care replaced with tubes 301a, b, c. A stepped, primary feed roller 302is used in place of feed roller 38 and a stepped secondary feed roller304 is used in place of feed roller 52. The stepped primary feed roller302 has three sections 306a, b, c of progressively increasing diameter,and the secondary feed roller 304 is formed with three identicalsections 308a, b and c. The tows 18a, b, c are first directed from thetubes 301a, b, c to the roller sections 306a, b, c of the stepped feedroller 302 where they are contacted by the pressure rollers 44a, b, c.The cylinder rod of each cylinder 48a, b, c is extended to theappropriate height so that the associated pressure rollers 44a, b, cconnected thereto contact the tows 18a, b, c, respectively. The tows18a, b, c are then fed to the respective sections 308a, b, c ofsecondary feed roller 304 where they are contacted by pressure rollers60a, b and c extended into position by their associated cylinders 64a,b, c. Each of the individual sections 306a, b, c of the primary feedroller 302 and sections 308a, b, c of secondary feed roller 304 isprovided with a separate material build-up sensor 92, only one of whichis shown in FIG. 1A for sections 306a and 308a.

As discussed in detail below in connection with a description of theoperation of this invention, the provision of sections 306a, b, c and308a, b, c of different diameter along the feed rollers 302, 304,respectively, results in the formation of chopped fibers 20 of differentlength from each tow 18a, b and c because the different diameters ofsuch sections 306a, b, c and 308a, b, c causes a different quantity ofmaterial to be advanced to the cutter mechanism 24.

Cutter Mechanism

Referring now to FIGS. 2-8, the cutter mechanism 24 of this invention isillustrated in detail. The cutter mechanism 24 is carried within arecess defined by an annular lip 110 at the top of the inlet cone 74mounted to the pump body 76 of venturi pump 22. The inlet cone 74 isalso formed with another inlet 75 which is adapted to connect to asource of lubricant, deodorant material or the like (not shown). Thecutter mechanism includes a cover plate 112 which mounts three, taperedtow guide tubes 114a, b, c each joined by a connector 116 to the towinlet tubes 72a, b, c, respectively. See also FIG. 1. An elongated, airinlet slot 118 is formed in the cover plate 112 adjacent each of theguide tubes 114a, b, c, and the cover plate 112 is also formed with acentral throughbore 120. Mounting holes 122 for screws or the like areformed in the cover plate 112 for supporting the assembled cuttermechanism 24 on the annular lip 110 of the pump inlet cone 74.

The cover plate 112 fits atop a cutter plate 124 having a top surface126 and a bottom surface 128. The cutter plate 124 is formed with astepped throughbore 130 at its center, and three, rectangular-shaped towslots 132a, b, c which are spaced approximately 120° from one another.These tow slots 132a, b, c align with the outlets of guide tubes 114a,b, c mounted on cover plate 112. An air slot 133 is formed in the cutterplate 124 adjacent each of the tow slots 132a, b, c, and these air slots133 align with the slots 118 formed in the cover plate 112. Preferably,the stepped throughbore 130 mounts a bearing 134 and a thrust washer 136for purposes described below. Cutter plate 124 is also formed withmounting holes 138 which align with the mounting holes 122 of coverplate 112.

As best seen in FIGS. 2 and 8, three protrusions or ribs 140a, b, c,spaced 120° apart, extend outwardly from the bottom surface 128 ofcutter plate 124 and are joined at the center thereof. Therectangular-shaped tow slots 132a, b, c extend through these ribs 140a,b, c, respectively, forming a shear edge 144 in each rib 140a, b, cwhich assist in the tow cutting operation described below.

Located adjacent the bottom surface 128 of cutter plate 124 is adouble-edged cutter blade 146 having two cutting edges 148 and 150oriented 180° from one another. The cutter blade 146 is formed with asquare throughbore 152 which mates with the square base 154 of a bladedrive shaft 156. As described in more detail below, the cutter blade 146is rotatable with respect to the ribs 140a, b, c at the bottom of cutterplate 124 to shear the tows 18a, b, c as they pass through tow slots132a, b, c against the shear edge 144 of the ribs 140a, b, c to formchopped fibers 12. Because the double-edge cutting blade 146 has cuttingedges spaced 180° apart, and the ribs 140a, b, c of cutter plate 124 arespaced 120° from one another, chopped fibers 12 are formed at each 60°of rotation of the cutting blade 146. This produces a steady,essentially continuous supply of chopped fibers 12 of uniform lengthfrom each tow 18a, b, c for discharge from the venturi pump 22 asdescribed below.

In assembling the cutter mechanism 24, the blade drive shaft 156 extendsupwardly through the square throughbore 152 so that its square base 154mates with the square throughbore 152 in cutter blade 146. The bladedrive shaft 156 passes through the stepped throughbore 130 in cutterplate 124 to receive the bearing 134 and thrust washer 136 carriedtherein. The blade drive shaft 156 then extends through the centralthroughbore 120 of cover plate 112, and a compression spring 158 isplaced over the blade drive shaft 156 between the thrust washer 136seated on top of bearing 134 within the stepped throughbore 130 incutter plate 124 and a spring locking ring 160. This spring locking ring160 has a set screw 162 to support it on the blade drive shaft 156. Byadjusting the position of the spring locking ring 160 along drive shaft156, the upwardly directed force exerted by the spring 158 on the bladedrive shaft 156 is varied thus altering the pressure with which thecutter blade 146 engages the ribs 140a, b, c of cutter plate 124. Theupper end of blade drive shaft 156 is mounted by a set screw 164 withina collar 166. This collar 166 has a set screw 168 which mounts the driveshaft 170 of a variable speed cutter motor 172 connected by line 174 tothe motor control 30. Rotation of the motor drive shaft 170 istransmitted through collar 166 to the blade drive shaft 156, which, inturn, rotates the cutter blade 146 along the bottom surface 128 ofcutter plate 124 relative to the ribs 140a, b, c extending therefrom.

Several aspects of the operation of cutter mechanism 24 are important inobtaining clean and accurate cutting of the tows 18a, b, c to formchopped fibers 12 which are substantially uniform in length and whichcan be transmitted without bunching up through the venturi pump 22. Oneimportant feature of the cutter mechanism 24 is the configuration of theguide tubes 114a, b, c. As viewed in FIGS. 2-6, each guide tube 114a, b,c has a generally circular inlet 176, and a rectangular-shaped outlet178. These outlets 178 have substantially the same dimensions, and arelocated in alignment with, the tow slots 132a, b, c in the cutter plate124. Each guide tube 114a, b, c tapers radially inwardly from its inlet176 to the rectangular-shaped outlet 178 for the specific purpose ofspreading or flattening the tows 18a, b, c in the course of passagetherethrough. As viewed in FIG. 4, the tow 18a, for example, has agenerally circular cross section when it initially enters the inlet 176of guide tube 114a wherein the individual strands 20 forming tow 18a arebunched together. In the course of passage through guide tube 114a, thetow 18a is formed to open or spread out in a generally elliptical shape.See FIG. 5. As viewed in FIG. 5, the individual strands 20 begin toseparate from one another within the tow 18a and move into aside-by-side relationship. When the tow 18a reaches therectangular-shaped outlet 178 of guide tube 114a, the individual strands20 are separated even further from one another and are more nearlyoriented side-by-side as compared to their relative position upon entryinto guide tube 114a. See FIG. 4. The same is true for tows 18b and c.

The purpose of separating the individual strands 20 of tows 18a, b, c,and orienting them generally side-by-side, is to obtain a relativelyprecise cut of each tow. If the individual strands 20 are bunched up andstacked behind one another, i.e., as they would be if cut when orientedas in FIG. 4, the individual strands 20 tend to be crushed against oneanother and not cleanly and individually sheared. By separating theindividual strands 20 from one another and orienting them generallyside-by-side, as viewed in the sequence of FIGS. 4-6, essentially eachindividual strand 20 is contacted by a cutting edge 148 or 150 (FIG. 8)thus ensuring clean separation of a chopped fiber 12 from the remainderof the tow 18a (and tows 18b, c), and the production of chopped fibers12 of uniform length.

Another feature of the cutter mechanism 24 of this invention whichcomprises an important aspect of this invention is the configuration ofthe ribs 140a, b, c at the bottom of the cutter plate 124 and theconstruction of the cutter blade 146. Because the individual strands 20of the tows 18a, b, c are very light and difficult to manipulate whencut, it has been found advantageous and important to cut all of thestrands 20 within a given tow 18 simultaneously, and then provide a flowpath for the newly formed chopped fibers 12 in a direction away from thecutter plate 124 and cutter blade 146 toward the outlet of the venturipump 22. This is accomplished in the cutter mechanism 24 of thisinvention by the movement of the cutter blade 146 with respect to thetow slots 132a, b, c and ribs 140a, b, c. As shown in FIG. 8, the cutterblade 146 is mounted for rotation with respect to the ribs 140a, b, c ofcutter plate 124 such that the cutting edges 148, 150 of cutter blade146 are oriented substantially parallel to the shear edges 142, 144formed by the tow slots 132a, b, c in ribs 140a, b, c when cutting agiven tow 18. Movement of either cutting edge 148 or 150 of the cutterblade 146 against the shear edge 144 therefore results in thesimultaneous shearing or cutting of essentially all of the strands 20within a given tow 18a, b, c, as opposed to, for example, ascissors-type cutting action in which the individual strands 20 would becut one at a time.

The reason for cutting all of the strands 20 within a given tow 18simultaneously is to avoid the formation of a gap or flow path between acutting edge 148 or 150 of cutter blade 146 and the shear edge 144formed by tow slots 132a, b, c in ribs 140a, b, c. If such a gap orspace was allowed to form, and the individual strands 20 within the tows18a, b, c were cut one at a time, the newly formed chopped fibers 12would tend to move toward such open space or gap creating bunching ofthe chopped fibers 12 thereat. Because the tows 18a, b, c are opened inthe course of passage through the guide tubes 114a, b, c, as discussedabove, their individual strands 20 are relatively uniformly spreadacross essentially the entire length of one of the shear edges 144 ofribs 40a, b, c in preparation for cutting. As viewed in FIG. 8, forexample, the vacuum applied by the venturi pump 22 within each tow slot132a, b, c, in combination with the counterclockwise movement of thecutter blade 146 with respect to such tow slots 132a, b, c, forces theindividual strands 20 of tow 18a against the shear edge 144 of tow slot132a immediately prior to a cutting operation. A small, uniform gap istherefore formed between the cutting edge 150 and shear edge 144 of rib140a, while the remainder of the tow slot 132a in rib 140a is covered bythe cutter blade 146. Immediately after the strands 20 of tow 18a aresimultaneously cut, the vacuum within guide tube 114a and tow slot 132ais momentarily interrupted because the cutter blade 146 advances to aposition in which it covers the entire tow slot 132a. With all of thechopped fibers 12 from tow 18a formed simultaneously, and with theentire tow slot 132a momentarily covered, essentially the only flow pathfor movement of the newly formed chopped fibers 12 is away from thecutter plate 124 and cutter blade 146 under the influence of thenegative pressure produced by the venturi pump 22. As a result, thechopped fibers 12 are cleanly severed from tow 18a and substantiallyseparated from another to prevent bunching up in the area of the cutterblade 146 and/or cutter plate 124. This ensures a substantially uniformand constant volume supply of chopped fibers 12 is discharged from theventuri pump 22.

While the configuration of the cutter mechanism 24 described above iseffective to direct the chopped fibers 12 into the venturi pump 22, itis recognized that there may be at least some accumulation of choppedfibers 12 on the cutter blade 146. The inlet slot 118 in cover plate112, and the aligning air slots 133 in cutter plate 124, collectivelyprovide an air flow path for ambient air which is drawn by the venturipump 22 onto the cutter blade 146 as it rotates. This air floweffectively cleans the cutter blade 146 of chopped fibers 12 which arethen directed into the venturi pump 22 for discharge.

Venturi Pump

Referring now to FIGS. 9-13, the venturi pump 22 of apparatus 10 isillustrated in more detail. As mentioned above, the function of theventuri pump 22 is to create a continuous vacuum which draws the tows18a, b, c from the secondary feed roller 52 into the cutter mechanism 24to form the chopped fibers 12. The venturi pump 22 can also be operatedintermittently, in sequence with the secondary feed roller 52 or 304, toprovide a vacuum when the tows 18a, b, c are intermittently fed thereto.In either mode of operation, chopped fibers 12 are emitted from theoutlet 82 of venturi pump 22 for supply to a system of the typeschematically illustrated in FIG. 14 and described below.

In the presently preferred embodiment, the venturi pump 22 comprises apump body 76 formed with an inlet passageway 180 which mounts the inletcone 74 described above in connection with cutter mechanism 24. Theinlet passageway 180 intersects a throughbore 182 formed in the pumpbody 76 having opposed ends which form the inlet 78 and outlet 82 ofventuri pump 22.

In order to develop a negative pressure within the inlet passageway 180,a nozzle 194 is mounted at the inlet end of inlet passageway 180 and aventuri insert 184 having a venturi passageway 186 is mounted at itsoutlet end. A number of different configurations of nozzles areillustrated in FIGS. 9-12, each of which direct a stream of pressurizedair past the inlet passageway 180 and into a venturi passageway 186formed in the venturi insert 184. As shown in FIG. 9, the venturi insert184 is preferably formed with a flange 187 which engages the pump body76 so that the inner end 188 of the venturi passageway 186 within insert184 extends into the throughbore 182 substantially flush with the inletpassageway 180, and so that the discharge outlet 190 of venturipassageway 186 extends outwardly from the pump body 76.

The nozzle 194 illustrated in FIG. 9 comprises a nozzle body 196 havingan outer end formed with a flange 198 which rests against the pump body76, and an inner end 200 which extends into the path of the inletpassageway 180. The nozzle body 196 is formed with a stepped, centralthroughbore 202, the inlet end of which is formed with an air inletwhich is threaded to receive a fitting (not shown) connected to the airline 80 from controller 28. The nozzle 194 is effective to discharge apressurized stream of air through its central throughbore 202, past theinlet passageway 180 and into the venturi passageway 186 of the venturiinsert 184. This pressurized air stream creates a vacuum or negativepressure within inlet passageway 180 which is transmitted through inletcone 74 to the guide tubes 114a, b, c associated with cutter mechanism24 and the tow inlet tube 72a, b, c which receive the tows 18a, b, cfrom the secondary feed roller 52.

In an alternative embodiment illustrated in FIG. 9A, a modified venturiinsert 320 is provided which mounts the discharge flow sensor 108. Asmentioned above, the discharge flow sensor 108 is preferably of the sametype as flow sensors 88a, b, c located upstream from the primary feedrollers 38 or 302 and the flow sensors 104a, b, c located upstream fromthe cutter mechanism 24 and venturi pump 22. As shown in FIG. 9A, theventuri insert 320 is a cylindrical-shaped tube, preferably formed ofaluminum or other electrically conductive material, having a venturipassage 322 and an external flange 324. When connected to the venturipump 22, the flange 324 of venturi insert 320 engages the pump body 76so that the inner end 326 of the venturi passage 322 within the insert320 extends into the throughbore 182 in the venturi pump body 76substantially flush with the inlet passageway 180, and so that thedischarge outlet 328 of venturi passage 322 extends outwardly from thepump body 76.

In the presently preferred embodiment, the flow sensor 108 comprises ahollow, cylindrical-shaped fitting 330 which is carried on the outer endof the venturi insert 320 as shown in FIG. 9A. An electricallyconductive ring 332, preferably formed of aluminum or the like, is pressfit into the fitting 330 and is sandwiched between a pair ofnon-conductive rings 334 and 336 preferably formed of nylon or otherdielectric material. The non-conductive ring 334 abuts the outer end ofventuri insert 320 and the non-conductive ring 336 abuts an electricallynon-conductive conduit, hose or tube 338. The fitting 330 is formed withdrilled and tapped holes, two of which overlie the venturi insert 320and the other two of which overlie the tube 338. These holes receive setscrews 342 which mount the fitting 330 to both the venturi insert 320and tube 338.

In the presently preferred embodiment, a single drilled and tapped hole344 is formed in approximately the center of fitting 330, in alignmentwith the conductive ring 332, and this hole 344 receives an electricalcontact 346 connected by a line 109 to the controller 28. In response tomovement of the tows 18a, b, c or fibers 20 through the flow sensor 108,or flow sensors 88a, b, c and flow sensor 104a, b, c, an electrostaticcharge is produced within the conductive insert 320 and conductive ring332. This electrostatic charge, in essence, is grounded through thecontact 346 and line 109. The magnitude of the electrostatic chargeproduced within the insert 320 and ring 332 is indicative of the rate atwhich the tows 18a, b, c or fibers 20 pass through the flow sensor 108and such charge is sensed by the controller 28 and compared to apredetermined value to ensure that the material passes through the flowsensor 108 at the desired rate.

Another embodiment of a nozzle 206 is illustrated in FIG. 10. Nozzle 206comprises a nozzle body 208 formed with a flange 210 at one end whichengages the pump body 76, and an elongated, nozzle tip 212 at theopposite or inner end. The nozzle body 208 and nozzle tip 212 are formedwith a stepped throughbore 214 having a larger diameter inlet portion216 including a threaded air inlet nozzle body 208, and a smallerdiameter outlet portion 218 within the nozzle tip 212 which terminatesat a discharge outlet 220. The nozzle 206 of FIG. 10 is oriented withrespect to the pump body 76 shown in FIG. 9 such that its nozzle tip 212extends into the venturi passageway 186 of venturi insert 184 when thenozzle 206 is mounted in place within the pump body 76. The nozzle 206is connected to the air line 80 from controller 28, and is effective todirect a stream of pressurized air from the discharge outlet 220 of itsnozzle tip 212 directly into the venturi passageway 186 of venturiinsert 184 to create a negative pressure within the inlet passageway180.

A still further embodiment of a nozzle 224 is illustrated in FIGS. 11and 11A. Nozzle 224 comprises a nozzle body 226 having an outer endformed with a flange 228 and an inner, internally threaded end 230 whichmounts a nozzle tip 232. The nozzle tip 232 includes a threaded flangeportion 233 which mounts to the threaded end 230 of nozzle body 226, anda substantially cone-shaped extension 234. A central portion 235 of thenozzle body 226 extends beyond its outer end 230 and engages thecone-shaped extension 234 of nozzle tip 232, with an O-ring 236 beingprovided therebetween to create a seal. The nozzle body 226 is formedwith a central throughbore 238 which is connected to a centralthroughbore or discharge passageway 240 formed in the cone-shapedextension 234. A second passageway 242 is formed in the nozzle body 226,substantially parallel to the central throughbore 238 therein, and thispassageway 242 terminates in an annular chamber 244 formed in the flangeportion 233 of the nozzle tip 232. The annular chamber 244 communicateswith a plurality of outlet ports 248 formed in the flange portion 233 ofnozzle tip 232 which are radially spaced from the central throughbore ordischarged passageway 240 of the cone-shaped extension 234 and arecircumferentially spaced from one another. See FIG. 11A.

The central throughbore 238 and passageway 242 of nozzle body 226 areconnected at their respective air inlets to lines (not shown) to thecontroller 28 to receive pressurized air therefrom. One stream ofpressurized air passes through the central throughbore 238 in nozzlebody 226, and the central throughbore or discharged passageway 240 inthe cone-shaped extension 234, directly into the venturi passageway 186of venturi insert 184. Another stream of air is transmitted through thepassageway 242 in nozzle body 226, into the annular chamber 244 in theflange portion 233 of nozzle tip 232 and then through the outlet ports248 therein. This produces an essentially cylindrical-shaped stream ofair which flows generally concentric to the cone-shaped extension 234 ofnozzle tip 232 and to the stream of air discharged from the centralthroughbore 240 of extension 234. These two streams of air enter theventuri insert 184 and create a negative pressure within inletpassageway 180.

The nozzle 250 illustrated in FIG. 12 is similar to that of FIG. 11except for the elimination of a central throughbore. Nozzle 250comprises a nozzle body 252 having an outer end formed with a flange254, and a threaded inner end 255 which mounts to a threaded flangeportion 258 of a nozzle tip 256 having a cone-shaped extension 260. Thenozzle body 252 is formed with a passage 262 having an inlet end formedwith an air inlet which is connected to the pressurized air lineconnected to controller 28, and an inner end which communicates with achamber 266 formed in the flange portion 258 of nozzle tip 256. Aplurality of outlet ports 268 are formed in the flange portion 258, incommunication with the chamber 266, and these outlet ports 268 arepreferably radially spaced from the longitudinal axis of the cone-shapedextension 260 and are circumferentially spaced from one another in thesame manner as depicted in FIG. 11A. Pressurized air is directed throughthe passage 262 from controller 28, enters the chamber 266 and is thendischarged through the outlet ports 268 directly into the venturipassageway 186 of venturi insert 184.

The nozzles 194, 206, 224 and 250 illustrated in FIGS. 9-12,respectively, are examples of presently preferred embodiments of a meansfor directing a stream of pressurized air past the inlet passageway 180of venturi pump 22 and into the venturi insert 184, or, alternatively, anon-venturi discharge tube 270 of the type schematically depicted inFIG. 13. In addition to the creation of negative pressure within theinlet passageway 180, each of these nozzles is intended to provide anair flow within the inlet passageway 180, throughbore 182 and theventuri passageway 186 of venturi insert 184 which assists in creatingat least some aeration and separation between the individual choppedfibers 12 produced by the cutter mechanism 24. Such separation isadvantageous in order to reduce bunching up of the chopped fibers 12 andobtain a relatively constant flow rate or volume of chopped fibers 12discharged from the venturi pump 22.

It is contemplated that the different configurations of the nozzlesherein are more advantageously utilized in different sprayingconditions. For example, the nozzles 194 and 206 illustrated in FIGS. 9and 10 may be more useful in applications where greater feed rates ofthe chopped fibers 12 are required. On the other hand, nozzles 224 and250 of FIGS. 11 and 12 may be more advantageously used in lower volumeapplications. It should be understood that the various configurations ofthe nozzles illustrated in FIGS. 9-12 are not intended to be exhaustive,but are given as examples of configurations which are useful in theventuri pump 22 to convey chopped fibers 12 of the type discussedherein.

Operation of System

For purposes of the present discussion, the operation of apparatus 10 isdescribed in connection with the supply of highly moisture-absorbentchopped fibers 12 into a forming chamber 272 of the type used to makethe nonwoven layer or pad 14 of a disposable diaper. The details offorming chamber 272 are disclosed in U.S. Pat. Nos. 4,927,346 and5,017,324, assigned to the assignee of this invention, the disclosuresof which are incorporated by reference in their entireties herein.Briefly, the forming chamber 272 includes an inlet 274 and an outlet276. The conveyor 32, mentioned above, is preferably an endlessperforated conveyor, carried by three rollers 280a, b, c, which ismovable through the forming chamber 272 between its inlet 274 and outlet276 in the direction indicated by the arrows in FIG. 14. The conveyor 32is movable over a duct 282 mounted at the base of forming chamber 272which is connected to a vacuum source 284.

A nonwoven material supply conduit 286 is connected to the conveyoroutlet end of forming chamber 272 at a position above the conveyor 32.The conduit 286 is connected to a source (not shown) of fibrousmaterial, preferably in the form of fibers or fluff 288 such ascellulose fluff, wood pulp, textile fibers or other fibrous material.The fluff 288 is pulled into the forming chamber 272 and drawn onto theconveyor 32 by operation of the vacuum source 284. As illustrated inFIGS. 14 and 15, vacuum is applied within the duct 282 which causes thefluff 288 to be drawn onto the conveyor 32 between the inlet end offorming chamber 272, where the duct 282 begins, and the outlet end offorming chamber 272 where the duct 282 ends. As the conveyor 32 movesthrough the forming chamber 272, the thickness of the intertwined fluff288 drawn onto the conveyor 32 gradually increases from a point ofminimum thickness near the chamber inlet 274 where the vacuum isinitially applied, to a point of maximum thickness toward the chamberoutlet 276. Preferably, a leveling or scarfing roller 290 is rotatablymounted within the forming chamber 272 near its outlet 276 to remove anupper portion of the fibers and form a nonwoven pad 14 having thedesired finish thickness.

In this particular application of forming the nonwoven pad 14 of adisposable diaper within forming chamber 272, the apparatus 10 functionsto introduce highly moisture-absorbent chopped fibers 12 into theforming chamber 272 where they are intermixed with a selected portion ofthe fluff 288 being drawn onto the conveyor 32 to form a nonwoven pad 14in which the highly moisture-absorbent chopped fibers 12 areinterspersed throughout a portion of the thickness of the pad 14 whilemaintaining other portions of the thickness of the pad 14 substantiallyfree of chopped fibers 12. It can be appreciated that in the applicationof forming disposable diapers, a reliable, constant volume supply orquantity of chopped fibers 12 is critical in order to ensure that suchpad 14 has the desired moisture-absorbency without introducing aninordinate amount of highly moisture-absorbent material therein.

The operation of the apparatus 10 depicted in FIG. 1 to achieve this endproceeds as follows. Initially, the speed of operation of apparatus 10is correlated to the speed of the conveyor 32 moving through the formingchamber 272 so that the appropriate amount of chopped fibers 12 aresupplied to the nonwoven pad 14 being formed within the forming chamber272. The operator control 26 is provided for this purpose and controlsthe speed of the conveyor 32, as well as the operation of controller 28and motor control 30 as described above. To begin operation, theoperator control 26 signals controller 28 to operate the primary motor42 driving primary feed roller 38 and the secondary motor 58 drivingsecondary feed roller 52 at the desired speeds. As described below, thepressure rollers 44a, b, c associated with primary feed roller 38, andthe pressure rollers 60a, b, c associated with secondary feed roller 52,are all moved to their extended positions such that the tows 18a, b, care forced against the primary and secondary feed rollers 38, 52 topositively feed them from their respective hoppers 34a, b, c to thecutter mechanism 24 of venturi pump 22. The venturi pump 22 operates toprovide a continuous negative pressure or vacuum within the tow inlettube 72a, b, c and guide tubes 114a, b, c associated with cuttermechanism 24 such that the tows 18a, b, c are positively drawn from thesecondary feed roller 52 into the cutter mechanism 24 and venturi pump22. The cutting operation described below is performed by the cuttermechanism 24, and the chopped fibers 12 are then transmitted through andout of the venturi pump 22 as described below.

In the embodiment of FIGS. 14-16, the chopped fibers 12 are dischargedfrom the venturi pump 22 through a conduit 192 and into the formingchamber 272. As discussed in detail in U.S. Pat. Nos. 4,927,346 and5,017,324, the outlet end 193 of conduit 192 is oriented with respect tothe nonwoven fibers or fluff 288 being drawn onto the conveyor 32 suchthat the highly moisture-absorbent chopped fibers 12 are intermixed witha portion of the fluff 288 being drawn onto the conveyor 32 thusproducing a nonwoven pad 14 in which the highly moisture-absorbentchopped fibers 12 are located in a predetermined portion of thethickness of the pad 14. The portion of pad 14 in which the highlymoisture-absorbent chopped fibers 12 and fluff 288 are intermixed isschematically illustrated as a thickness 292 in FIG. 15, whereas theareas 294 and 296 forming the remainder of pad 14 are substantially freeof the highly moisture-absorbent chopped fibers 12.

It has been found that in the formation of a nonwoven pad 14 fordisposable diapers, chopped fibers 12 of highly moisture-absorbentmaterial provide a number of advantages. The chopped fibers 12 tend tobecome substantially intertwined with nonwoven fibers or the fluff 288within the pad 14 which substantially reduces loss or migration of thehighly moisture-absorbent material either through the perforatedconveyor 32 within forming chamber 272 or at the outer surfaces of thenonwoven pad 14 such as against the polyethylene backing sheet (notshown) of a finished disposable diaper. Additionally, the chopped fibers12 of highly moisture-absorbent material have a relatively large surfacearea, compared to highly moisture-absorbent material in particulateform, and therefore moisture or body fluids are readily and quicklyabsorbed by the highly moisture-absorbent fibers 12.

It should be understood that while the chopped fibers 12 are illustratedas being located predominantly within a center layer or area 292 withinthe thickness of the nonwoven pad 14, the chopped fibers 12 could belocated essentially anywhere within the thickness of pad 14 as describedin detail in U.S. Pat. Nos. 4,927,346 and 5,017,324. Alternatively, theconduit 192 could be attached directly to the nonwoven material inletconduit 286 such that the highly moisture-absorbent chopped fibers 12are completely interspersed with the nonwoven material 288 as it entersthe forming chamber 272, thus forming a nonwoven pad 14 in which thehighly moisture-absorbent chopped fibers 12 are interspersed throughoutthe entire thickness of the nonwoven pad 14.

As mentioned above and schematically illustrated in FIG. 16, theapparatus 10 of this invention is capable of intermittently dischargingchopped fibers 12 from the venturi pump 22. In order to obtainintermittent discharge of chopped fibers 12, the controller 28 signalsmotor control 30 to intermittently operate the secondary motor 58associated with secondary feed roller 52. The secondary motor 58 iseffective to start and stop the rotation of secondary feed roller 52which controls the supply of tows 18a, b, c into the cutter mechanism 24and venturi pump 22. The secondary feed roller 52 can be intermittentlystopped and started without damaging tows 18a, b, c because of theexcess length or loop 54 of each tow 18a, b, c formed between theprimary feed roller 38 and secondary feed roller 52, described above.Accordingly, the tension of the tows 18a, b, c at the secondary feedroller 52 remains constant whether the secondary feed roller 52 isoperated continuously or intermittently. If desired, the venturi pump 22can also be operated intermittently, i.e., when the secondary feedroller 52 supplies the tows 18a, b, c thereto, so that a vacuum isalways applied to the tows 18a, b, c when they are advanced from roller52. Intermittent operation of secondary feed roller 52 produces anonwoven pad 14 of the type shown in FIG. 16 wherein the highlymoisture-absorbent chopped fibers 12 are located at longitudinallyspaced areas 298 along the length of the pad 14.

It is contemplated that in most instances wherein the apparatus 10 isemployed to form a nonwoven pad 14, the venturi pump 22 will becontinuously operated. As a result, an essentially constant flow of airis introduced into the forming chamber 272, at a predetermined locationrelative to the nonwoven pad 14 being formed, which carries anintermittent supply of air-entrained chopped fibers 12. By providing acontinuous air flow into the forming chamber 272, instead of anintermittent or pulsed flow of air-entrained chopped fibers 12, it isbelieved that there is less disruption in the movement of the fluff 288onto the conveyor 32 and a more accurate distribution of chopped fibers12 within the desired area or portion of the thickness of the nonwovenpad 14.

An important aspect of the operation of apparatus 10 is its capabilityof providing an essentially constant volume or quantity of choppedfibers 12 in the event the supply of one or more of the tows 18a, b, cis interrupted, terminated or otherwise varies from a predetermined feedrate. As discussed previously, the progress of each tow 18a, b, cthrough the apparatus 10 is individually monitored by a variety ofsensors. Movement or flow sensors 88a, b, c are provided for each tow18a, b, c upstream from primary feed roller 38, sensors 104a, b, c arelocated at the entrance to tow inlet tubes 72 and a flow sensor 108 iscarried at the outlet 82 of pump body 76. Material level sensors 84a, b,c are provided for each tow 18a, b, c at their respective hoppers 34a,b, c, and a loop detection sensor 100 are provided for each tow 18a, b,c to detect the loop 54 thereof formed between the primary and secondaryfeed rollers 38, 52. Each of these sensors 88, 104, 108 and 100 providessignals to the controller 28 as described previously to monitor thefeed/flow rate or movement of the tows 18a, b, c, or chopped fibers 12,compared to predetermined levels.

In the event of a termination, interruption or other variation in thesupply of one or more of the tows 18, an operational sequence isinitiated by controller 28 to maintain a substantially constant quantityof the chopped fibers 12, of the same length, for discharge through theventuri pump 22. For purposes of discussion, assume that the tow 18a hasbecome severed somewhere in between its hopper 34a and the cuttermechanism 24. One or more of the sensors 88a, 100a, 104a or 108 willsend a signal to the controller 28 indicating that the movement or flowof tow 18a has fallen below a predetermined level. Because one-third ofthe supply of material to the cutter mechanism 24 of venturi pump 22 isno longer present, the controller 28 is operative to "make up" orcompensate for that loss by increasing the rate of supply of the othertwo tows 18b and c.

Initially, the controller 28 actuates the pneumatic clamp 68a associatedwith tow 18a to clamp the remainder of tow 18a in place upstream fromthe cutter mechanism 24 and venturi pump 22. The controller 28 signalsmotor control 30 to operate the primary motor 42 and secondary motor 58which increase the speed of operation of the primary feed roller 38 andsecondary feed roller 52, respectively. Assuming the same quantity ofchopped fibers 12 is required, the speed of rotation of each of theprimary and secondary feed rollers 38, 52 is increased fifty percent tomake up for the loss of supply of tow 18a. In order to maintain the samelength of chopped fibers 12 as had been obtained with all three tows18a, b, c, the controller 28 signals the motor control 30 to speed upthe operation of cutter motor 172. This increases the speed of rotationof the cutter blade 146 so that it is correlated with the increasedspeed of tows 18b and c passing through the cutter mechanism 24 andventuri pump 22. As a result, the chopped fibers 12 produced from onlytows 18b and c are of substantially the same length as those producedwhen all three of the tows 18a, b, c are directed through cuttermechanism 24.

As mentioned below, material build-up sensors 92 are provided for eachof the primary and secondary feed rollers 38, 52, and material build-upsensors 94a, b, c are provided for each of the pressure rollers 44a, b,c associated with primary feed roller 38 and each of the pressurerollers 60a, b, c associated with secondary feed roller 52. It iscontemplated that in the event the individual strands 20 forming thetows 18a, b, c become adhered to either of the primary or secondary feedrollers 38, 52, as sensed by material build-up sensors 92, operation ofapparatus 10 will have to be temporarily discontinued in order to clearsuch feed rollers 38, 52 of material. However, if a material build-upoccurs on any one of the pressure rollers 44a, b, c or pressure rollers60a, b, c, as sensed by material build-up sensors 94a, b, c, it iscontemplated that a sequence of the type described above could beinitiated. For example, if the pressure roller 44a associated with tow18a became covered with material, the controller 28 would be operated toactivate both pneumatic cylinders 48a and 64a to move the pressureroller 44a and 60a, respectively, to a retracted position away fromtheir respective feed rollers 38, 52. The same sequence of operationwith respect to the speed up of tows 18b and c and cutter motor 172described above would then be initiated, while an operator was clearingeither one of the pressure rollers 44a or 60a of material.

The apparatus 300 of this invention depicted in FIG. 1A operates in theidentical manner as described above for apparatus 10 except for therelative quantities of chopped fibers 20 produced from each of theindividual tows 18a, b and c. As discussed above, apparatus 300 differsfrom apparatus 10 in that a stepped primary feed roller 302 is providedhaving sections 306a, b and c of different diameter, and an identicallyconfigured stepped secondary feed roller 304 is provided with sections308a, b and c. As depicted in FIG. 1A, the sections 306a, b and c of theprimary feed roller 302 progressively increase in diameter so that inresponse to rotation of motor shaft 40 the smaller diameter section 306arotates over a shorter distance, because of its smaller circumference,than the section 306b or section 306c. As a result, a greater quantityof tow 18c from the largest circumference section 306c passes to thecutter mechanism 24, compared to tows 18b and 18a, and the choppedfibers 20 produced from tow 18c are therefore longer than those producedfrom tow 18b, which, in turn, are longer than those produced from tow18a.

The apparatus 300 of the embodiment of FIG. 1A therefore provides forthe supply of different quantities of chopped fibers, having differentlengths, depending upon the requirements of a particular application.For example, in the application of forming disposable diapers 14 it maybe desirable to introduce different super-absorbent materials, eachhaving different properties such as varying wicking capacity or thelike, wherein it is preferred to have a larger quantity of one materialthan another. In such an application, one or more of the tows 18a, b andc could be formed of one type of super-absorbent material and another ofthe tows 18a, b, c could be formed of another super-absorbent materialsuch that the desired relative quantity of such materials, in the formof chopped fibers 20 of different length, could be produced anddispensed from the venturi pump 22 into the forming chamber 272.

While the invention has been described with reference to a preferredembodiment, it should be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof.

For example, the sequence of operation of apparatus 10 described aboveto accommodate the loss or interruption in the supply of one of the tows18a involves an increase in feed rate of each of the other tows 18b andc to maintain a substantially constant feed rate or volume of choppedfibers 12 for discharge from the venturi pump 22. It is contemplatedthat such sequence of operation could also, or alternatively, include aslow down of the line speed of conveyor 32 within forming chamber 272,in the particular embodiment disclosed in FIG. 14, which would beeffected by the operator control 26.

In addition, the cutter plate 124 is shown with a bottom surface 128having three protrusions or ribs 140a, b, c against which the cutterblade 146 shears the tows 18a, b, c. It is contemplated that the bottomsurface 128 could be flat, thus eliminating the ribs 140a, b, c,although the cutter blade 146 would essentially continuously rub orengage such surface and may wear more quickly.

The operation of apparatus 10 has also been described in connection withthe supply of highly moisture-absorbent chopped fibers 12 into a formingchamber 272 having a conveyor 32. It should be understood that otherforming chamber constructions could be employed, including those havinga drum-type pad support.

Therefore, it is intended that the invention not be limited to theparticular embodiment disclosed as the best mode contemplated forcarrying out this invention, but that the invention will include allembodiments falling within the scope of the appended claims.

It is claimed:
 1. Apparatus for forming and dispensing chopped fibersfrom continuous tows, comprising:a pumping unit having an inlet and adischarge outlet; a cutter mechanism connected to said inlet of saidpumping unit; feed means for feeding a first tow into said cuttermechanism and for selectively feeding a second tow into said cuttermechanism, said cutter mechanism including cutter means for cutting eachof said first and second tows to form chopped fibers of predeterminedlength which are directed into said pumping unit; sensor means forsensing movement of each of said first and second tows to said cuttermechanism, and for producing a signal in the event the feed rate of oneof said first and second tows varies from a predetermined feed rate;control means connected to said sensor means and to said feed means forreceiving a signal from said sensor means indicative of a variation inthe feed rate of one of said first and second tows to said cuttermechanism, and for operating said feed means to correspondingly vary thefeed rate of the other of said first and second tows to said cuttermechanism so that a substantially constant feed rate of chopped fibersis emitted from said discharge outlet of said pumping unit.
 2. Theapparatus of claim 1 in which said pumping unit is a venturi pumpcomprising:a pump body formed with an inlet passageway and a throughborehaving opposed ends, said inlet passageway intersecting said throughborebetween said opposed ends thereof; a nozzle mounted at one end of saidthroughbore, said nozzle having at least one air inlet for removableconnection to a source of pressurized air for directing a stream of thepressurized air toward said other end of said throughbore and past saidinlet passageway in said pump body; a venturi insert having a venturipassageway, said venturi insert being mounted at said other end of saidthroughbore in position to receive said stream of pressurized air withinsaid venturi passageway thereof which creates a negative pressure withinsaid inlet passageway to draw chopped fibers therethrough.
 3. Theapparatus of claim 2 in which said nozzle comprises a nozzle body and anelongated nozzle tip, said nozzle body and nozzle tip being formed witha stepped throughbore having a larger diameter portion within saidnozzle body and a smaller diameter portion within said nozzle tip, saidnozzle tip at least partially extending into said venturi passageway ofsaid venturi insert.
 4. The apparatus of claim 2 in which said nozzlecomprises:a nozzle body having at least two of said air inlets; saidnozzle body formed with a central throughbore and a second passagewayradially spaced from said central throughbore, said central throughboreand said second passageway each being connected to one of said airinlets; a nozzle tip mounted to said nozzle body, said nozzle tip beingformed with a discharge passageway which connects to said centralthroughbore of said nozzle body, and a plurality of outlet ports whichare radially spaced from said discharge passageway and circumferentiallyspaced from one another, said outlet ports communicating with saidsecond passageway in said nozzle body.
 5. The apparatus of claim 4 inwhich said nozzle tip has a flange portion connected to a cone-shapedextension which tapers radially inwardly from a larger diameter end atsaid flange portion to a smaller diameter end, said outlet ports beingformed in said flange portion of said nozzle tip and said dischargepassageway having a discharge outlet at said smaller diameter end ofsaid cone-shaped extension.
 6. The apparatus of claim 2 in which saidnozzle comprises:a nozzle body defining said at least one air inlet andhaving a bore connected to said at least one air inlet; a nozzle tipmounted to said nozzle body having a flange portion and a cone-shapedextension, said flange portion of said nozzle tip being formed with aplurality of spaced outlet ports which are radially spaced relative tosaid cone-shaped extension and circumferentially spaced from oneanother, said outlet ports communicating with said bore in said nozzlebody.
 7. The apparatus of claim 1 in which said feed means comprises:atleast one feed roller; drive means for rotating said feed roller; afirst pressure roller and a second pressure roller each movable withrespect to said feed roller between an extended position and a retractedposition, said first pressure roller in said extended position beingeffective to force said first tow against said feed roller to advancesaid first tow to said cutter mechanism, said second pressure roller insaid extended position being effective to force said second tow againstsaid feed roller to advance said second tow to said cutter mechanism. 8.The apparatus of claim 7 in which said first and second pressure rollersare movable independently of one another.
 9. The apparatus of claim 7 inwhich said control means, in response to the receipt of said signal, isoperable to:(i) move one of said first and second pressure rollerscorresponding to said one of said first and second tows, respectively tosaid retracted position while maintaining the other of said first andsecond rollers in said extended position; and (ii) operate said drivemeans to increase the speed of rotation of said feed roller so that saidother of said first and second tows is advanced at an increased feedrate to said cutter mechanism.
 10. The apparatus of claim 9 furtherincluding clamping means located between said feed roller and saidpumping unit for clamping said one of said first and second tows in afixed position with respect to said cutter mechanism.
 11. The apparatusof claim 1 in which said first and second tows are each formed of aplurality of essentially continuous strands, said cutting meansincluding:a cutter plate having a first surface and a second surface,said cutter plate being formed with first and second tow slots eachextending from said first surface to said second surface; first andsecond guide tubes each having an inlet and an outlet aligned with saidfirst and second tow slots, respectively, in said cutter plate, saidfirst and second guide tubes tapering inwardly from said inlet to saidoutlet thereof so that said individual strands forming said first andsecond tows are at least partially separated from one another andoriented generally side-by-side upon entry into said first and secondtow slots formed in said cutter plate; a cutter blade operably mountedproximate said cutter plate and having at least one cutting edge, saidcutter blade being rotatable with respect to said cutter plate so thatsaid at least one cutting edge thereof shears substantially all of saidstrands within said first and second tows at said first and second towslots to form said chopped fibers.
 12. The apparatus of claim 11 inwhich said cutter plate is formed with first and second ribs extendingoutwardly from said second surface thereof, said first and second towslots each extending from said first surface through said first andsecond ribs, respectively, and being rectangular in shape forming anelongated shear edge in each of said first and second ribs, said cutterblade being movable relative to said rectangular tow slot in each ofsaid first and second ribs such that said cutting edge of said cutterblade is oriented substantially parallel to said elongated shear edge ofsaid rectangular tow slots upon cutting of said first and second towswhile the remainder of said rectangular tow slot in each of said firstand second ribs is substantially covered by said cutter blade to preventthe passage of pressurized fluid therethrough.
 13. The apparatus ofclaim 11 in which said cutter plate is formed with an air slot adjacenteach of said first and second tow slots, said pumping unit beingeffective to draw air through said air slots to remove chopped fibersfrom said cutter blade.
 14. The apparatus of claim 11 further includinga third tow, a third guide tube having a tow inlet and a tow outletaligned with a third tow slot in said cutter plate, said first, secondand third guide tubes and tow slots being spaced approximately 120° fromone another.
 15. The apparatus of claim 14 in which said at least onecutting edge of said cutter blade comprises two cutting edges spaced180° apart, said cutter blade being rotatable with respect to saidcutter plate so that chopped fibers are produced from said first, secondand third tows at each 60° of rotation of said cutter blade. 16.Apparatus for forming and dispensing chopped fibers from continuoustows, comprising:a pumping unit having an inlet and a discharge outlet;a cutter mechanism connected to said inlet of said pumping unit; feedmeans for feeding a first tow into said cutter mechanism at a first rateand for selectively feeding a second tow into said cutter mechanism at asecond rate, said cutter mechanism including cutter means for cuttingsaid first tow to form chopped fibers of one length and for cutting saidsecond tow to form chopped fibers of another length, said chopped fibersbeing directed into said pumping unit; sensor means for sensing movementof each of said first and second tows to said cutter mechanism, and forproducing a signal in the event the feed rate of either of said firstand second tows varies from said first and second feed rates,respectively; control means connected to said sensor means and to saidfeed means for receiving a signal from said sensor means indicative of avariation in the feed rate of one of said first and second tows to saidcutter mechanism, and for operating said feed means to correspondinglyvary the feed rate of the other of said first and second tows to saidcutter mechanism so that a substantially constant feed rate of choppedfibers is emitted from said discharge outlet of said pumping unit. 17.The apparatus of claim 16 in which said feed means comprises:at leastone feed roller, said feed roller being formed with a stepped outersurface including a first section having a first diameter and a secondsection having a second diameter; drive means for rotating said feedroller; a first pressure roller and a second pressure roller eachmovable with respect to said feed roller between an extended positionand a retracted position, said first pressure roller in said extendedposition being effective to force said first tow against said firstsection of said feed roller to advance said first tow to said cuttermechanism, said second pressure roller in said extended position beingeffective to force said second tow against said second section of saidfeed roller to advance said second tow to said cutter mechanism.
 18. Theapparatus of claim 17 in which said first and second pressure rollersare movable independently of one another.
 19. Apparatus for forming anddispensing chopped fibers from continuous tows, comprising:a pumpingunit having an inlet and a discharge outlet; a cutter mechanismconnected to said inlet of said pumping unit; feed means for feeding afirst tow into said cutter mechanism and for selectively feeding asecond tow into said cutter mechanism, said cutter mechanism includingcutter means operative at a predetermined rate for cutting each of saidfirst and second tows to form chopped fibers of predetermined lengthwhich are directed into said pumping unit; sensor means for sensingmovement of each of said first and second tows to said cutter mechanism,and for producing a signal in the event the feed rate of one of saidfirst and second tows varies from a predetermined feed rate; controlmeans connected to said sensor means, to said feed means and to saidcutter mechanism for:(i) receiving a signal from said sensor meansindicative of a variation in said feed rate of one of said first andsecond tows to said cutter mechanism; (ii) operating said feed means tovary the feed rate of the other of said first and second tows to saidcutter mechanism in accordance with said variation in the feed rate ofsaid one tow; and (iii) varying the speed of operation of said cuttingmeans of said cutter mechanism, whereby substantially the same volume ofchopped fibers, being substantially said predetermined length, isemitted from said discharge outlet of said pumping unit.
 20. Theapparatus of claim 19 in which said first and second tows are eachformed of a plurality of essentially continuous strands, said cuttingmeans including:a cutter plate having a first surface and a secondsurface, said cutter plate being formed with first and second ribsextending outwardly from said second surface thereof, and first andsecond tow slots each extending from said first surface through saidfirst and second ribs, respectively; first and second guide tubes eachhaving an inlet and an outlet aligned with said first and second towslots, respectively, in said cutter plate, said first and second guidetubes tapering inwardly from said inlet to said outlet thereof so thatsaid individual strands forming said first and second tows are at leastpartially separated from one another and oriented generally side-by-sideupon entry into said first and second tow slots formed in said cutterplate; a cutter blade operably mounted proximate said cutter plate andhaving at least one cutting edge, said cutter blade being rotatable withrespect to said cutter plate so that said at least one cutting edgethereof shears substantially all of said strands within said first andsecond tows at said first and second ribs to form said chopped fibers.21. The apparatus of claim 20 in which each of said elongated tow slotsis rectangular in shape forming an elongated shear edge in each of saidfirst and second ribs, said cutter blade being movable relative to saidrectangular tow slot in each of said first and second ribs such thatsaid cutting edge of said cutter blade is oriented substantiallyparallel to said elongated shear edge of said rectangular tow slots uponcutting of said first and second tows while the remainder of saidrectangular tow slot in each of said first and second ribs issubstantially covered by said cutter blade to prevent the passage ofpressurized fluid therethrough.
 22. The apparatus of claim 19 in whichsaid cutter plate is formed with an air discharge means adjacent each ofsaid first and second tow slots for directing a stream of air to removechopped fibers from said cutter blade.
 23. The apparatus of claim 19further including a third tow, a third guide tube and a third tow slotin said cutter plate, said first, second and third guide tubes and towslots being spaced approximately 120° from one another.
 24. Theapparatus of claim 23 in which said at least one cutting edge of saidcutter blade comprises two cutting edges spaced 180° apart, said cutterblade being rotatable with respect to said cutter plate so that choppedfibers are produced from said first, second and third tows at each 60°of rotation of said cutter blade.